So I did a little bit of online reconnaissance and came up with a nice little ride on the North side of the park.
North Park is North of Pittsburgh in the North Hills. From Pittsburgh take 279 to McKnight road and take McKnight up past the Ross Park mall. Bear right onto Babcock Blvd after the Peebles road intersection.
To get there take Babcock along the South end of the lake and turn North onto Pierce Mill Road. Pearce Mill Road runs along the lake. Up past the end of both North Park Lake and Marshall Lake there is a trail head opposite where Kummer road enters Pearce Mill Road.
The ride is pretty much all single track, not too technical, but has a steep climb. There's a lot of fun fast paced stuff once you get up on the ridge.
This trail begins where Kummer Road meets Pearce Mill Road and parallels North Ridge Road.
Park at the basketball courts on Kummer Road. [View on Google Maps]
Make a right out of the parking lot and go about 300 yards and bear right at the Y, staying on Kummer Road and cross the creek. As the bend straightens Brown road merges onto Kummer. Go about another 50 yards you will come to a triangle where Kummer road ends at Pearce Mill Road. Take the left fork of the triangle and the trail head is directly in front of you.
The trail head is directly in front of you, however unless your are in top shape I would recommend taking North Ridge Road to the top of the hill. The initial climb is manageable but it takes you down into a ravine and the second climb to the trail summit is very long (about 1/2 mile) and fairly steep. The trail is 100% climbable but it's long and doesn't let up much. Making this climb bottom to top without a rest is truly a physical and technical challenge.
Ok if you decide you are taking the road make a right onto Pearce Mill Road going South. Take this road 300 yards and make a left up the hill onto North Ridge Road. North Ridge road will climb for nearly half a mile.
After the trail summits it comes down and meets North Ridge road. If you are taking the road this is where you want to pick it up.
Follow the trail as is parallels North Ridge Road, there will be a couple of trail intersections and you'll want to keep right. This will take you to a picnic area at the top of the ridge point. Keep going and the trail will begin a fast but gradual descent. The trail merges onto another trail Look for the a trail on your right and take this uphill for a longer ride. Either direction will take to you to the down stream end of North Park Lake near the boat launch.
The best way back is to take the lower trail along the lake inlet. There is a section too steep the climb but this way gives you the best ride and least amount of walking. Keep an eye out for where you originally merged onto this trail on our way in. Take this branch up to the picnic area else you'll end up walking your bike up a very steep unpleasant and muddy section of trail. From there just backtrack.